Among various heat transfer techniques so far known in the art, there is proposed a sublimation type of transfer system wherein a sublimable dye as a recording material is carried on a substrate sheet such as paper or a plastic film to make a heat transfer sheet, which is in turn overlaid on a heat transfer sheet dyeable with a sublimable dye, for instance, a heat transfer sheet comprising paper or a plastic film having a dye-receiving layer on its surface to make various full-color images thereon. In this system, the thermal head of a printer is used as heating means to transfer three-, four- or more-color dots by a very quick heating, thereby reconstructing a full-color image of the original by the multi-color dots.
Because the coloring material used is a dye, the thus formed image is so clear and so excellent in transparency that the resulting image representation can be improved in the reproducibility of halftone and gray scale. This makes it possible to form image representations similar to those achieved with conventional offset or gravure printing and comparable in quality to full-color photographic images.
A problem with the thus obtained image representations, however, is that because of being formed of a dye, they are generally so inferior in light fastness to pigmented images upon being exposed directly to sunlight, they fade or discolor prematurely. Some solution to such a light fastness problem may be provided by adding ultraviolet absorbers or antioxidants to the dye-receiving layers of heat transfer image-receiving sheets. Yet image storability presents an important problem to be solved.